This account traces a lecture given to El Colegio Nacional last March during a Conference "On the origin of life on the Earth" organized to celebrate Darwin's Bicentennial. It reports on the extraterrestrial organic materials found in carboncontaining meteorites, their composition, likely origin and possible prebiotic contribution to early terrestrial environments. Overall, this abiotic chemistry displays structures as diverse as kerogenlike macromolecules and simpler soluble compounds, such as amino acids, amines and polyols, and show an isotopic composition that verifies their extraterrestrial origin and lineage to cosmochemical synthetic regimes. Some meteoritic compounds have identical counterpart in the biosphere and encourage the proposal that their exogenous delivery to the early Earth might have fostered molecular evolution. Particularly suggestive in this regard are the unique Lasymmetry of a number of amino acids in some meteorites as well as the rich and almost exclusively watersoluble compositions discovered for other meteorite types.

I am grateful to Professor Eusebio Juaristi, Guillermo DelgadoLamas and Antonio Lazcano for their invitation and the opportunity to visit the Colegio Nacional. I also thank an anonymous referee for a very helpful review. These studies were supported through the years by grants from the Exobiology, Cosmochemistry and Origins of the Solar System programs of the US National Aeronautic and Space Administration.

References

1. In a letter to Joseph Hooker (1871), Darwin famously wrote: "It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (and oh! what a big if! ) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present, that a proteine compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly absorbed, which would not have been the case before living creatures were found".